Clinical Applications of Blood-Derived Extracellular Vesicle Biomarkers in Breast Cancer: A Scoping Review.

Blood-derived extracellular vesicle (EV) biomarkers have emerged as promising liquid-biopsy analytes for monitoring treatment response and prognosis in breast cancer. This scoping review mapped the clinical evidence on blood-derived EV in breast cancer and identified key barriers to clinical translation. Following the Joanna Briggs Institute framework and PRISMA-ScR guidelines, we searched PubMed, Embase, and Web of Science for eligible studies published through November 2025. After duplicate removal, title and abstract screening, and full-text assessment, 64 clinical studies were included. Research activity increased markedly from 2020 onward, accounting for 87.5% (56/64) of included studies. The literature was concentrated in East Asia, particularly China (51.6%, 33/64). RNA-based biomarkers predominated (60.9%, 39/64), especially microRNAs (39.1%, 25/64). Prognostic outcomes were evaluated in 89.1% (57/64) of studies, treatment response in 51.6% (33/64), and both endpoints in 40.6% (26/64). Triple-negative breast cancer was the most frequently studied subtype in isolation (15.6%, 10/64). Methodological heterogeneity was substantial, and kit-based precipitation was the most common EV isolation method (57.8%, 37/64). EV biomarkers show promise for non-invasive monitoring in breast cancer, but methodological standardization, compliance with Minimal Information for Studies of Extracellular Vesicles guidelines, and large prospective validation studies remain necessary before routine clinical implementation.